An inflator for inflating an inflatable vehicle occupant protection device, such as an air bag, contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated so as to ignite the body of gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired to help protect a vehicle occupant. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
It is desirable that the gas generating material for inflating an inflatable vehicle occupant protection device meet a number of technical requirements. For instance, the gas generated by combustion of the gas generating material should be substantially free of toxic materials. It should also preferably be essentially smoke-free. The gas generating material must be chemically and physically stable over a wide temperature range, and should have ignition and combustion characteristics suitable for use with a vehicle occupant protection device.
The gas generating material preferably contains a fuel which has a favorable oxygen balance. A fuel with a favorable oxygen balance reduces the weight percent of oxidizer needed to oxygen balance the gas generating material and to avoid, upon combustion, excessive production of carbon monoxide.
High energy organic compounds with favorable oxygen balances such as cyclotrimethylenetrinitramine (RDX) and cyclotetramethylenetetranitramine (HMX) have been proposed for use as fuels in gas generating materials for inflators. U.S. Pat. No. 5,125,684 discloses a gas generating material that comprises HMX or RDX, an oxidizer salt, and a cellulose based binder. The advantage of HMX or RDX in the formulation is that gas effluent from combustion of the formulation is smokeless. However, high energy organic compounds with favorable oxygen balances such as HMX or RDX are sensitive to external stimuli including external heat, impact, friction and electrostatic discharge.